1. Field of the Invention
The present invention relates to displays, and in particular relates to driver circuits of displays.
2. Description of the Related Art
FIG. 1 is a schematic diagram illustrating a driver circuit in the prior art. The driver circuit 100 comprises a pixel 102 and an output stage 104 for driving the pixel 102. The output stage 104 of the driver circuit 100 further comprises a p-type MOSFET (PMOS) 112 and an n-type MOSFET (NMOS) 114, and each of the transistors 112 and 114 comprises a gate coupled to a pixel signal Sp and controlled by the pixel signal Sp to switch an output voltage Vout on the pixel between a high level VH and a low level VGND.
The output voltage Vout on the pixel 102 and characteristic of a display influences the brightness of the pixel. Taking a carbon nanotube display (CNDP) for example, owing to its particular characteristics, the brightness of the carbon nanotube display will increase as the carbon nanotube display ages. For this reason, it is necessary for the driver circuit 100 to have a calibration device 130 to calibrate the brightness of the carbon nanotube display. For example, in the calibration device 130 in FIG. 1, the transmission gate composed of a PMOS T1 and an NMOS T2 is controlled by a bias voltage Vbias to calibrate an equivalent resistance of the calibration device 130 to further calibrate brightness level of the pixel 102.
However, the coupling effect of the transistor T1 (due to the coupling capacitor between the gate and the source/drain) makes the output voltage Vout reversely influence the bias voltage Vbias, as shown in FIG. 2. The output voltage Vout on the pixel 102 alternates between two voltage levels according to the pixel signal SP. When the output voltage Vout switches from the low voltage VGND to the high voltage VH, the output voltage makes the bias voltage Vbias rise sharply and causes a surge P1 therein. When the output voltage Vout switches from the high voltage VH to the low voltage VGND, the output voltage makes the bias voltage Vbias fall sharply and causes a surge P2 therein. In addition, because the driver circuit 100 of the display is a high voltage device, a high voltage VH on the pixel 102, may be as high as 110 volts. Once the bias voltage Vbias changes, the equivalent resistance of the calibration device 130 accordingly changes, thus causing luminance flicker on the display.